Almost 12 million Americans suffer from insulin dependent diabetes mellitus (IDDM), and the attendant hyperglycemia in these patients appears to account for a majority of microvascular and neurologic complications. To eliminate the need for constant glucose monitoring in diabetic patients, a number of cellular replacement strategies have been proposed. But such approaches will ultimately require a basic understanding of the mechanism by which insulin gene expression is regulated both constitutively and in response to glucose. Within the insulin promoter, two AT rich motifs termed FLAT and P appear to be critical for high level expression of the insulin gene in beta islet cell lines. We have recently characterized a novel pancreatic homeobox factor, referred to as STF-1, which binds to the FLAT and P elements and which stimulates insulin promoter activity in heterologous cells. In this proposal we will test whether STF-1 is a principal regulator of insulin gene expression in pancreatic beta cells. I. To test whether STF-1 is indeed critical for insulin gene expression, we will inhibit STF-1 activity by microinjection of STF-1 antisera into beta islet cells and by immunodepletion of in vitro transcription extracts. We will further test this hypothesis by expressing anti-sense STF-1 RNA in stably transfected beta islet cell lines. II. Recent evidence suggesting that STF-1 can stimulate insulin gene expression in heterologous cells by cooperating with the basic helix loop helix factor E47 has prompted us to test the mechanism by which these two proteins interact to stimulate high level expression of the insulin gene. III. Like other tissue-specific regulators, STF- 1 is expressed primarily in pancreatic islet cells, and we will analyze the STF-1 promoter to identify cis-acting elements and cognate factors which target STF-1 expression to these cells. Based on recent evidence that STF-1 mRNA accumulation is rapidly inhibited by glucocorticoids, we will further examine whether dexamethasone interferes with STF-1 promoter activity and thereby inhibits insulin gene expression. A number of patients receiving chronic glucocorticoid therapy (i.e. rheumatoid arthritis) often develop symptoms of insulin deficiency, and our studies may identify STF-1 as an important target for glucocorticoid action in the pancreas.